In recent years, environmental regulations are becoming more and more stringent on a global scale. In particular, the circumstances surrounding automobiles, including fuel efficiency requirements and exhaust emission regulations, are becoming increasingly difficult. Behind this, there are environmental issues, such as global warming, and resource protection arising from concerns about the depletion of petroleum resources. For these reasons, it is believed that further reduction of fuel consumption in automobiles will be pursued. To reduce fuel consumption in automobiles, improvement of engine oil, such as reduction of viscosity thereof or addition of a good friction modifier for the purpose of reducing friction loss in an engine, is as important as improvement of automobiles per se, such as weight reduction of automobiles or engine improvement.
For example, Patent Document 1 discloses a lubricating oil composition for an internal combustion engine with a high-temperature high-shear viscosity at 150° C. of 2.6 mPa·s and a high-temperature high-shear viscosity at 100° C. of 5.5 to 5.9 mPa·s which is obtained by adding a polymethacrylate-based viscosity index improver, a salicylate-type metal detergent and a molybdenum-based friction modifier to a mineral oil-type base oil having a relatively low viscosity, enabling to improve fuel efficiency in an internal combustion engine.